It is a common practice in the art to prepare coatings for substrates as thin films. Many substrates may be coated on one or several of its surfaces. For example, an optical or ophthalmic substrate may be coated on one or both of its major opposing surfaces. The coatings may include a single coating or a plurality of coatings, many, most or all of which impart to the finished substrate improvements in surface, optical and/or mechanical properties. One such coating for a substrate is an anti-reflective (AR) coating. AR coatings are thin films applied to reduce reflectivity. The AR coating when complete typically includes more than one, and up to four or six or more single thin layers that form a so-called “stack.” Some of the layers in the stack may be of differing materials and some of the layers in the stack may be of differing refractive indices. When applied to many substrates, such as polymer substrates, the one or plurality of layers may be arranged on top of a surface coating, often referred to as a hard coating, one that has already been applied to the substrate.
A number of processes and methods have been developed to apply the AR coating (of one or more layers) on the substrate. The substrate, which can include an ophthalmic article, can be a finished or semi-finished substrate (e.g., coated, partially coated, or uncoated). The substrate may of any type. The substrate may be light transmissive or non-transmissive. For ophthalmic articles, the substrate is a transparent material, such as a glass material, gemstone, or a composite (e.g., polymer). Coatings are then applied on the exposed substrate surface, ensuring that the desired order of the final thin film or stack includes a layer on or closest to the substrate and then outwardly therefrom. One or more layers may be applied to both a rear and front surface of a substrate. For an ophthalmic article, such as a lens, the rear surface is generally the concave surface and, when applied to a lens for a wearer's eye, will be the surface of the substrate closest to a wearer's eye. The front surface for an ophthalmic article, such as a lens, is generally the convex surface and, when applied to a lens for a wearer's eye, will be the surface of the substrate farthest from the wearer's eye.
A conventional process for applying an AR coating (as one or more materials in one or more layers) involves manually pouring a single raw material into a cup of a crucible positioned in a rotating hearth of a vacuum chamber, as described further herein. An operator can pour the same material into multiple cups, as needed, or may pour different raw materials into different cups. This process may be repeated if there is more than one cup in the crucible. For example, eight cups can be loaded with materials in order to coat one side of a lens. The process then further involves sequentially accessing and evaporating at least a portion of the raw materials from the cup. Typical raw materials can include, for example, SiO2, MgF2, Al2O3, TiO2, ZrO2, Ta2O5, and similar materials, or blends of these raw materials that are manufactured by a supplier. Evaporating includes an energetic electron beam used to heat one of the raw materials in a pocket to a sufficient temperature such that at least a portion of the raw material is evaporated, and the evaporated material is then deposited onto the surface of the lens substrate.
There are several disadvantages with the above described process. It requires significant operator skill and is prone to operator error. For example, an operator is sometimes required to carefully manage the amount of raw material placed into the cup, i.e., under-filling, over-filling, and/or levelling may occur, which is both time consuming and wasteful. The operator may be required to go back to the cup with additional material in order that the raw material is the right amount, such that it is flush with the outer edge of the cup. This process is both hard to control and can have a detrimental effects on product quality. Other problems with this method may include spillage and overflow of material due to lack of control by the operator, when pouring or re-pouring the raw material(s) into the cups. Overtopping or jamming the crucible can also occur, requiring tool maintenance and can compromise the equipment. Any of these issues increase operator time in an already lengthy process, and also introduce unreliability, inconsistency and a compromise in the quality of each layer and/or the final coating.
There remains a need to improve the AR coating process and the AR coating itself.